Piston



Dec. 1, 1936. e. D. WELTY PISTON 5 1 2 1 3 V. l u J 0 6 l i F V WNVENTOR BY in weight, having ample strength at all tempera- Patented Dec. 1, 1936- George Donald Welty, Cleveland, Ohio, assignor, by mesne assignments, to The Cleveland Trust Company, Cleveland, Ohio, a corporation of Ohio, trustee Application July 31, 1925, Serial No. 47,220 16 Claims. (Cl. soap-13) This invention relates to pistons for internal combustion engines, particularly pistons composed of metal having a coeflicient of expansion greater than that of iron.

By my invention I am enabled to construct a piston which may be characterized as being light tures, having substantially the same rate and amount of expansion and contraction in its skirt as the cylinder has in which it operates, having very low frictional resistance and correspondingly high efliciency, being comparably free from the accumulation of dense carbon deposits and preignition troubles, having a substantially uniform bearing over the entire length and breadth of the bearing portions at all temperatures, having little or no tendency to collapse and thus increase the original clearance, having relatively very wide orcircumferentially extended bearing portions, say, to and being capable of operating with an extremely small amount of actual wear as compared with similar pistons of the prior art. Moreover, by my invention 1' have constructed a piston in which the diameters or .chordal dimensions at the lateral edges ofsthe bearing faces expand at a lesser rate and to a lesser degree than the intermediate diameters and dimensions of the bearing faces.

In the drawing accompanying this application I and forming a part of this specification:

Fig. 1 is a side elevation of one form of piston embodying my invention;

Fig. 2 is a vertical section taken, substantially on line 2-2 of Fig. 1; I

Fig. 3 is an open end view of the piston shown in Fig. 1;

Figs. 4 and 5 are, respectively, side elevation and top plan view of a hollow rectangle insert employed in the pistons of Figs. 1 to 3, inclusive. Referring to the figures, the piston consists of a head 2 and a skirt 3. The head 2 consists of an end disc 4 and a peripheral depending ring flange 4a., to opposite sides of which are connected depending boss carrying walls 5 forming a part of the skirt 3 and carrying bosses 6. The boss carrying walls 5 may be supportedby ribs 1 disposed within the piston and united with the inner surfaces of the disc 4 and the ring flange 4a. In the piston shown by these figures where the bosses 6 are supported at their inner ends by the walls or webs 5, it may be desirable to provide additional support for the bosses in the form of ribs ring flange as by air gaps l0, and which are separated from each other by splits ll disposed below the bosses. The bearing walls 9 are preferably, though not necessarily, cut away from below the bosses to their upper ends to expose the bosses 6 5 and webs 5. Flexible arches or webs l2 span the splits II and resiliently connect the bearing walls 9 together below the bosses. The bearing walls 9 are connected to the boss carrying webs 5 by flexible, resilient, distortable webs or connectors 10 l3 which in the piston shown join the bearing walls al g the longitudinal side edges thereof. It will b understood that the webs or arches l2 and I3 are by reason of their shape and size capable of being distorted to permit movement of 15 either bearing wall 9 with respect to the other bearing wall or remaining parts of the piston. The webs l3, however, are sufllciently rigid to withstand the side thrust forces imposed upon the bearing walls 9 when the piston is in operation in as an engine. l 7. Means are associated with the bearing walls 9 to overcome the natural action of the piston under temperature changes and to control the walls in the operationof the piston under vary- 25 ing conditions of temperature. This-means comprises a metal insert, strut or connector which preferably, though not necessarily, is composed and 5and consists of a plate of metal rectangular in shape and formed .with a central opening to provide spaced vertical arms and spaced horizontal portions. Preferably as shown, the central opening in the member I4 is substantially rectang ular so as to reduce the weight to a minimum. In a slightly br'oader aspect of the invention the functions of the insert or strut are independent of the exact shape of the insert or of the opening therein, and I therefore also use the term link to describe the hollow inserts or struts. As shown, each hollow rectangle insert I4 is shown cast into both bearing walls 9, and with its'lugs Ila cast into a boss 6 and arib, 8. The member l4 lies substantially parallel to, but is spaced apart from, the boss carrying webs -5, although it will be understood by those skilled in the, art that this member may also lie in substantial contact with the outer surface of the webs 5. v

The piston, with the exception of the insert, is preferably composed of light metal, for example-aluminum or magnesium alloys, while the inserts I4 are preferably composed of material such as iron or steel or any other material having substantially the same coefficient of expansion as the metal of the cylinder in which the piston is to operate.

My theory of the operation of the piston shown is as follows:

The piston is fitted into its cylinder with a clearance of approximately one thousandth of an inch per inch of cylinder diameter. As the piston becomes heated in operation in the cylinder, the head expands, carrying outwardly with it the boss carrying walls 5. These walls tend to move the portions of the members H in contact therewith outwardly with them, this tendency being in part counteracted by slight bending of the members l4. Inasmuch as the members 14 are fixedly secured to or embedded in the bearing walls 9 like chain links, the tendency to diametrical expansion or contraction of the bearing walls 9 is counteracted by the slower and smaller rate of expansion of the members l4, which is due to the lower coeificlent of expansion of the material composing these members. Furthermore, since the anchoring of the members l4 in the walls 9 is sufficiently strong and since the'dimensions of members M are so proportioned that the tensile strength of the members will exceed the force necessary to cause distortion of the flexible webs I 3, the tendency to diametrical expansion and contraction of walls 9 will be limited and controlled by the members H, the webs I3 being dis-. torted as the temperature increases and restored to their normal position or lengthened therebeyond as the temperature decreases. The flexible or dlstortable webs or connectors 13 may thus be thought of as expansion joints connecting the bearing walls 9 and the boss carryingwebs which take up the diammetrical expansion of cross members 9 in excess of the lengthwise expansion of the members l4. Buckling of the inserts i4 is prevented in part by the lugs Ma thereon which are embedded in the casting.

Circumferential and diametrical expansion of the bearing walls 9 is in part counteracted by the members Hand results in a slight alteration of the original truly. circular surface of these walls and in a slight bowing out of the bearing walls intermediatetheir junctions, with the members M, as is indicated by a slightly greater amount of wear and a visibly heavier bearing on the surfaces of these bearing walls intermediate these members M. The longitudinal sides of the bearing walls 9 are, contrary to practice heretofore, apparently retracted slightly as the piston is heated to normal operating temperatures, or permitted to expand more slowly and to less degree, as is indicated by a slightly decreased amount of wear along these side edges and opposite the ends of members l4, and/or by a visibly lighter bearing. The difference in wear has, however.

been measurable only in smallfractions of thou-.

sandths-of an inch, even after such pistons have run for the equivalent of manythousand miles of car travel. It is thus evident that in contrast with pistons of the prior art having chordal boss carrying webs and marked wear opposite the ends ofsuch webs, I have produced a piston which, as'it is heated to operating temperatures, tends to change its original truly circular surface of the bearing walls of the skirt and to wear more at the center of the bearing faces than, opposite the ends of the chordal webs.

By reason of the control of the movements of the upper ends of the bearing walls by the insert, these walls tend to bear at all times on the cylinder wall with substantially the same force. Furthermore, since the greater tendency to diametrical expansion and contraction of the bearing walls 1sv at the upper ends thereof and since the flexible arches l2 are provided to accommodate diametrical changes in the lower ends of the bearing walls, it will be obvious that I have provided a piston in which the bearing walls not only bear throughout substantially their entire longitudinal and circumferential extent on the cylinbeen extended relatively far, say 90 to 110, in

a circumferential direction and in which the bearing force is not concentrated at any one part of the bearing walls.

Pistons embodying my invention have shown an amount of wear on the bearing surfaces measured in fractions of thousandths of an inch after many thousand car miles of travel, which is several hundred per cent less than the wear found in pistons of the prior art composed of similar material and tested under substantially the same conditions.

It will be understood that directional expressions as vertical and vertically, appearing in this specification and in the claims, refer to the positions of parts as shown on the drawing and do not necessarily describe the positions of those parts when the piston is man engine, for example, in a V-typeengine where the pistons reciprocate on lines having an about thirty degrees. J

Having thus described my invention, what I desire to secure by Letters Patent is defined in what is claimed. q

' What is claimed is:

1. A piston comprising a head, oppositely disposed boss carrying websdepending therefrom, oppositely disposed bearing walls separated from the head, flexible connectors joining the said wallsto the said webs, said connectors being flexible in a diametrical direction to permit rela- .tive movement of said bearing walls toward'and away from each other by flexing of said connectors, and a metal insert having a lower co efficient of expansion than the remaining parts of the piston disposed adjacent to each boss carrying web and each united with both bearing walls over a longitudinal length of the latter greater than the corresponding length of attachment of the bearing walls to the flexible conincluded angle of .ing webs in the region of the bosses, and a pair of chordal struts, one disposed adjacent to each of the bosses, having end edges embedded in said bearing walls for controlling the thermal expansion and contraction of the bearing walls and for causing flexing of the connectors under thermal changes.

4. A piston comprising ahead, oppositely dispo'sed chordal boss carrying webs depending therefrom, substantially semi-circular bearing walls connected by flexible means below the bosses and connected to the webs in the region of the bosses by flexible means, all of the said flexiblemeans being arranged to flex to permit relative movement of said bearing walls toward and away from each other the said bearing walls being cut away from below the bosses to their upper ends to expose the boss carrying webs, and two hollow rectangle inserts, one disposed adjacent to each boss and connected to the bearing walls, the said head, webs, flexible connecting means and bearing walls being composed of a metal' of a relatively high coefiicient of expansion as compared with that of the'metal of the hollow rectangles.

5. An aluminum piston for an internal combustion engine comprising a head, co-axial bosses carried by the head, oppositely disposed bearing walls separated from the head and supported from the bosses by aluminum connectors which are flexible in a direction perpendicular to the axis of said bosses to permit said bearing walls to move toward and away from each other, and means for limiting the expansion and contraction rates and amounts at the lateral edges of the bearing faces to less than the corresponding rates and amounts intermediate the said edges, said means including separate members of ferrous metal, each united to both bearing walls both above and below a boss and being flexible in a direction parallel to the axis of said bosses, said members and said aluminum connectors being arranged in such a manner as to convert the forces created by separation of said bosses upon expansion of said head into pulling forces at the lateral edges of said bearing faces tending to pull the lateral edges of the opposite bearing faces together.

6. In a piston for an internal combustion engine, the combination of a head having a top and a depending flange having ring grooves for the piston rings, a pair of wrist pin bosses suspended from said head and positioned diametrically opposite each other in the piston, a skirt for said piston comprising a pair of diametrically opposite thrust face portions, one of which at least is separated from the head, said piston being relieved about the bosses, said bosses being set within the periphery of the piston, the portions of the piston below the bosses being slitted longitudinally, bridges mounted on the inside of the piston and spanning said slits, said head, bosses, skirt and bridges being composed of a material of a relatively high co-eificient of expansion and connectors of a material of a relatively low co-efficient of expansion connecting said thrust face portions together, said connector's being arranged above and below the bosses and extending across said piston on chords thereof perpendicular or substantially perpendicular to the wrist pin axis, and each of said connectors having end edges embedded in said opposite thrust face portions.

7. A piston having a skirt with spaced thrust faces and a vertically disposed hollow rectangle link at each side of said skirt having one end or vertical arm embedded in each thrust face and surrounded by the material thereof and its sides extending between said ends or vertical arms.

8. A piston having a skirt with spaced bearing faces, a vertically disposed hollow rectangle link at each side of said skirt having one end or vertical arm embedded in eachbearing face and surrounded by the'materi'al thereof and its sides extending between said ends or vertical arms, and a wrist pin bearing between said sides and between said ends.

and below one wrist pin bearing, the sides being partly embedded in the bearing carrying walls.

11. In a piston for an internal combustion engine, the combination of a head and skirt of a material of a relatively high co-efiicient of heat expansion, means depending from the said head, piston pin bosses in said means, said skirt being separated from the head, chordal webs of the same material as the head and skirt uniting said skirt, with the piston pin bosses, chordal struts of a material of a lower co-eflicient of heat expansion than that of the head and skirt comprising separate plates arranged parallel with each other on opposite sides of the piston and embedded in said means, said struts being separated by air gaps from said chordal webs, said struts having ends terminating in the material of the adjacent parts of the skirt, substantially as set forth. I

12. In a piston for an internal combustion engine, the combination of a head and a skirt of a material of a relatively high co-eflicient of heat expansion, said head having integral means depending therefrom, piston pinbosses in the means, said skirt being separated from the head, chordal webs of the same material as the head and skirt uniting said skirt with 'the piston bosses, said skirt provided with a relatively narrow split in the lower part of the skirt, chordal struts of a material of a lower co-eflicient of heat expansion than that of the head and skirt and separated by an air gap from said .chordal webs, said struts being connected to said skirt on both sides of the bosses both above and below the terial of the adjacent parts of the skirt, substantially as set forth.

13. In a piston for an internal combustion engine, the combination of a head, piston pin bosses, a skirt, means connecting the same into an integral construction, said head, bosses, skirt and interconnecting means being of a material of a relatively high coefficient of heat expansion, said skirt and head being separated by air gaps,

- bosses and having end edges buried in the ma said skirt being provided in the lower portion thereof with a relatively narrow slit,,said skirt being provided with bearing faces and being cut away about the bosses, chordal struts of a lower coeflicient of heat expansion than the material of the said skirt connecting the bearing faces and the bosses together and extending in a horizontal direction across the cut away portions of the skirt, said struts comprising separate plates arranged substantially parallel with each other on opposite sides of the piston, said struts having end edges buried in the material of the adjacent parts of the skirt, substantially as set forth, means of relatively high coefficient of heat expansion connecting the bosses and the skirt also extending in a horizontal direction across the cut away portions of the skirt and separated by air gaps from the said chordal struts.

14. In a piston for an internal combustion englue, the combination of a head having a depending flange grooved on the outside for piston rings, a pair of webs depending from the head on opposite sides thereof and carrying aligned piston pin bosses, a skirt including a substantially cylindrical portion disposed below said bosses and spaced thrust faces extending upwardly from said substantially cylindrical portion be-- tween said bosses and being spaced at their upper edges from said flange, said head and skirt being composed of a material having a relatively high coeflicient of expansion, connectors of the same material as said head and skirt integrally connecting said skirt with said depending webs,

connectors composed of a material having a relatively low co-efiiclent of expansion separated from said first mentioned connectors by an air gap extending across the spaces between said thrust faces and embedded in said webs and having end edges embedded in said thrust faces, and connecting said thrust faces and said webs together above the axis of said wrist pin bosses and other connectors of a material having a relatively low coeflicient of expansion connecting said thrust faces together below the axis of said wrist pin bosses.

15. In a piston for an internal combustion engine, the combination of a head having a depending fiange grooved on the outside for piston rings, a pair of webs depending from the head on opposite sides thereof and carrying aligned piston pin bosses, a skirt including a substantially cylindrical portion disposed below said bosses and spaced thrust faces extending upwardly from said substantially cylindrical portion between said bosses and being spaced at their upper edges from said flange, said head and skirt being composed of a material having a relatively highco-eflicient of expansion, connectors of the same material as said head and skirt integrally connecting said skirt with said depending webs, and a pair of plates composed of a material having a relatively low cc-efilcient of expansion extending across the spaces between said thrust faces on opposite sides of the piston and connecting said thrust faces together and to said depending webs, each of said plates being apertured to form vertically extending arms at the ends thereof, each of said arms being integral at its opposite ends with a plate, said arms being embedded in and encircled by the material of the thrust faces.

16. A piston comprising a head, wrist pin bosses, and a skirt having opposed bearing faces spaced from the head, said parts being integral and composed of light metal alloy, and vertical hollow rectangular connectors, at the boss sides of the skirt, composed of metal of a lower coefficient of thermal expansion than that of said light metal alloy, each connector having vertical arms at its ends, said arms of each connector being embedded in and surrounded by the opposed bearing faces.

- GEORGE DONALD wEL TY. 

